1. Field of the Invention
The present invention relates to an image processing method for restoring the tonal picture from binary image (image restoring method). The gradation processing of an image, at least either the enlarging or reducing of images, and filtering (image emphasis, or the like), are effected on the basis of the image restoring method by an apparatus therefor.
2. Description of the Prior Art
A method of restoring processing images based upon binary data had not hitherto existed. As methods of enlarging (or magnification) or reducing (or reduction) the binary image relying upon the picture element density conversion system, there have been known an SPC method, an logical sum method, a divide-by-nine method, a projecting method, and the like.
It has not so far been possible to process binary data images. When the processing was not perfect, therefore, the image sensing was carried out a plurality of times while changing the image sensing conditions. moreover, it was not possible to process an image when there was no original image.
According to the conventional method of enlarging (or expanding) and reducing (or contracting) the binary image relying upon the picture element density conversion system, problems arise because lines are defaced or omitted. The greatest problem, however, is that Moire fringes develop when it is attempted to enlarge or reduce a half-tone image (tonal image) having perodic structure such as binary image expressed by an ordered dither matrix. This is because, sampling is effected twice, i.e., at the time of converting image signals into digital signals and at the time of expanding or contracting the image. Therefore, the image is often adversely affected depending upon the magnification. To eliminate this phenomenon, it has been contrived to express the image relying upon a random dither method which, however, results in complex circuitry. With the MAE method or the ED (Error Difusion) method, furthermore, a structure resembling a "striped domain" appears on the half-tone portion which some people find unpleasant. Therefore, these methods have not been placed in practical use.
In treating binary half-tone images of this kind, furthermore, no method had existed for easily effecting the filering and the gradation processing (conversion).
The conventional method of expanding or contracting the image relying upon the picture element density conversion system.has been employed in printers and in facsimile, as has been known to enlarge and reduce mainly the drawings and characters. When the methd of this type is adapted to the image having gradation, the magnification of an integer number of times is effected, and the pitch of the mesh after magnification is usually different. Further, when the image is to be magnified by a rational number of times, the image is adversely affected (Moire fringes develop) to such a degree that it is no longer used practically.